JP2006319441A - Photoelectric conversion apparatus, photoelectric conversion method, image reading apparatus, two-dimensional image sensor, and drive method of two-dimensional image sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric conversion apparatus from which a sufficient photoelectric conversion amount can be obtained, resulting in that an optimum sensitivity corresponding to a read speed of an original and an emission luminous quantity to the original can be obtained and to provide an image reading apparatus provided with the photoelectric conversion apparatus and a photoelectric conversion method. <P>SOLUTION: The photoelectric conversion apparatus charges up electric charges to an auxiliary capacitor 17 connected to a drain D of a TFT 7 including a photoelectric conversion element by a prescribed amount, brings the TFT 7 to a nonconductive state, emits light to the TFT 7 for a prescribed time after the electric charges by the prescribed amount applied to the auxiliary capacitor 17 is finished, and thereafter senses a photoelectric conversion amount of a sensor substrate 20 including the TFT 7 on the basis of the electric charges charged onto the auxiliary capacitor 17, and the photoelectric conversion apparatus includes a drive IC 19 for applying a gate voltage to a gate G of the TFT 7 when the TFT 7 is brought into the nonconductive state and the light is emitted to the TFT 7 for the prescribed time, and a control/communication board 24 for applying variable control to the gate voltage applied by the drive IC 19. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a photoelectric conversion device that detects the photoelectric conversion amount of a photoelectric conversion element, and in particular, an image reading device and a two-dimensional image that are suitably used for image reading in a personal computer, an information terminal, etc. using the photoelectric conversion device. It relates to sensors.

  Conventionally, an image reading apparatus (for example, an image scanner) combining a one-dimensional image sensor and mechanical scanning has been used for image input of a personal computer, a facsimile, or the like. In this case, it is necessary to move and scan the one-dimensional image sensor with respect to the document, or to move and scan the document, both of which need to be scanned mechanically. In addition, downsizing and weight reduction of the device have been limited.

  On the other hand, various contact-type two-dimensional image sensors that do not require mechanical scanning have been proposed. In many of these, one pixel is formed by a pixel selection transistor for preventing crosstalk and a photodiode or phototransistor as a photosensor, and each pixel is arranged in a two-dimensional matrix to form a two-dimensional image sensor. Is configured.

  However, as described above, a contact-type two-dimensional image sensor that does not require mechanical scanning is capable of high-speed image reading and can be reduced in weight and thickness. Therefore, many proposals have been made, but it has been put into practical use. There is no example.

  One of the main factors is the complexity of the pixel structure and the array structure. In other words, compared to TFT arrays used in mass-produced active matrix liquid crystal displays, the manufacturing process for forming photosensors increases, the pixel structure becomes complicated, and the pixel area increases. There is a problem that it is difficult to increase the resolution.

  Even when the photosensor itself has a photosensor function and a selection function, it has a complicated structure in which, for example, a reverse stagger type thin film transistor and a coplanar type thin film transistor are combined in a single semiconductor layer. The manufacturing process is complicated.

In order to solve the above problems, for example, Patent Document 1 discloses a phototransistor having a photosensitive semiconductor layer, a sensor substrate having an auxiliary capacitor connected to the drain electrode of the phototransistor, and the above A photoelectric conversion device is disclosed that includes a detection IC that is connected to a source electrode of a phototransistor and detects the amount of photoelectric conversion by the sensor substrate. In this photoelectric conversion device, a predetermined amount of charge is charged to the auxiliary capacitor, and charge generated by light irradiation to the photosensitive semiconductor layer when the phototransistor is in the non-conductive state is charged. The photoelectric conversion amount of the sensor substrate is detected based on the electric charge. Thereby, the pixel structure constituting the photosensor can be simplified, so that the number of usable pixels can be increased, and as a result, high resolution can be achieved. In addition, the manufacturing process can be simplified.
JP 2004-47618 (published February 12, 2004)

  However, in the photoelectric conversion device disclosed in Patent Document 1, the gate voltage applied to the gate electrode of the thin film transistor when the gate drive signal is at a low level is constant. ), The light conversion amount (sensitivity) may not be sufficiently obtained. Therefore, when such a photoelectric conversion device is applied to an image reading device, sufficient sensitivity cannot be obtained depending on the reading speed of the document and the amount of light applied to the document.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to obtain a sufficient amount of photoelectric conversion, and as a result, an optimum sensitivity corresponding to the reading speed of the document and the amount of light applied to the document. It is an object to provide a photoelectric conversion device that can be obtained, an image reading device including the photoelectric conversion device, and a photoelectric conversion method.

  As a result of intensive studies to solve the above problems, the inventor of the present application differs from FIG. 17 (Graph 1) and FIG. 18 (Graph 2) in that the gate-off voltage (Vgl voltage) of the TFT capable of obtaining the maximum sensitivity differs depending on the reading speed. I found out. Further, from FIG. 19 (Graph 3), it was found that the Vgl voltage of the TFT capable of obtaining the maximum sensitivity differs depending on the irradiation light amount (in the case of monochromatic light and in the case of multicolor light). That is, it was found that when the gate-off voltage value of the TFT was fixed, sufficient sensitivity could not be obtained depending on the reading speed and the amount of irradiation light.

  Here, the maximum sensitivity refers to the photocurrent of the thin film transistor that is irradiated with the strongest light within a period in which a plurality of thin film transistors are turned off and each photosensitive semiconductor layer is irradiated with light having different intensities. The difference between the value or the value accumulated therein and the photocurrent value of the thin film transistor irradiated with the weakest light or the value accumulated therein.

  Therefore, in order to solve the above-described problem, the photoelectric conversion device according to the present invention charges a predetermined amount of charge to the auxiliary capacitor connected to the drain electrode of the thin film transistor having the photosensitive semiconductor layer, and the predetermined amount to the auxiliary capacitor. After the charging of the charge is completed, the thin film transistor is made non-conductive, the photosensitive semiconductor layer is irradiated with light for a predetermined time, and the photosensitive semiconductor layer is irradiated with light for a predetermined time, and then based on the charge of the auxiliary capacitor. In the photoelectric conversion device for detecting the photoelectric conversion amount of the photoelectric conversion element including the thin film transistor, the gate electrode of the thin film transistor is applied to the gate electrode of the thin film transistor when the photosensitive semiconductor layer is irradiated with light for a predetermined time after the thin film transistor is turned off. Gate voltage applying means for applying a gate voltage, and gate for variably controlling the gate voltage applied by the gate voltage applying means. It is characterized by comprising a G Voltage control means.

  According to the above configuration, when the photosensitive semiconductor layer is irradiated with light for a predetermined time after the thin film transistor is turned off, the gate voltage variably controlled by the gate voltage control means is applied to the gate electrode. Therefore, the detected photoelectric conversion amount can be controlled.

  Thereby, a photoelectric conversion amount to be detected, that is, a gate voltage that maximizes the photocurrent flowing through the non-conducting thin film transistor can be applied to the gate electrode of the thin film transistor, so that a sufficient photoelectric conversion amount can be obtained. That is, a photoelectric conversion device that can obtain optimum sensitivity can be realized.

  In this case, the gate voltage control means sets the gate voltage to a value at which the maximum sensitivity can be obtained within the time when the thin film transistor is turned off and the photosensitive semiconductor layer is irradiated with light. do it.

  The value of the gate voltage set by the gate voltage control means is a value derived from the relationship between the irradiation time of light to the thin film transistor and the photoelectric conversion amount at that time when the thin film transistor is turned off. May be.

  The gate voltage control means causes the gate voltage application means to apply a reference gate voltage to the gate electrode of the thin film transistor, and sets the value of the gate voltage applied to the gate electrode from the photoelectric conversion amount detected at that time You may make it do.

  In order to solve the above problems, a photoelectric conversion method according to the present invention charges a predetermined amount of charge to an auxiliary capacitor connected to a drain electrode of a thin film transistor having a photosensitive semiconductor layer, and a predetermined amount of charge to the auxiliary capacitor. After the completion of charging, the thin film transistor is turned off to irradiate the photosensitive semiconductor layer with light for a predetermined time, and after irradiating the photosensitive semiconductor layer with light for a predetermined time, based on the charge of the auxiliary capacitor, In the photoelectric conversion method for detecting the photoelectric conversion amount of the photoelectric conversion element, when the thin film transistor is in a non-conducting state and the photosensitive semiconductor layer is irradiated with light for a predetermined time, a gate voltage that provides maximum sensitivity is set to the thin film transistor. It is characterized by being applied to the gate electrode.

  According to the above configuration, when the photosensitive semiconductor layer is irradiated with light for a predetermined time while the thin film transistor is in a non-conducting state, a gate voltage that provides maximum sensitivity is applied to the gate electrode of the thin film transistor. The detected photoelectric conversion amount, that is, the photocurrent flowing through the non-conducting thin film transistor is maximized.

  Therefore, it is possible to provide a photoelectric conversion method capable of obtaining the maximum sensitivity (photoelectric conversion amount) with an appropriate gate voltage corresponding to the light irradiation amount (irradiation time × light intensity) to the non-conducting thin film transistor. it can.

  In order to solve the above problems, an image reading apparatus according to the present invention includes a plurality of photoelectric conversion devices arranged in correspondence with a document image, and photoelectric conversion elements detected by each photoelectric conversion device. Image information output means for outputting the conversion amount as input image information of a document image is provided.

  According to the above configuration, since the photoelectric conversion device described above is provided, a sufficient amount of photoelectric conversion can be obtained, and as a result, optimum sensitivity corresponding to the reading speed of the document and the amount of light applied to the document can be obtained. it can.

  Thereby, input image information faithful to the document image can be output from the image information output means.

  Further, the document image includes light irradiating means for irradiating red light, green light, and blue light, respectively, and the image information output means is a photoelectric conversion element detected according to each color irradiation light by the light irradiating means. The input image information may be output as a color image from the photoelectric conversion amount.

  In this case, the gate voltage for obtaining the optimum sensitivity (photoelectric conversion amount) differs between the operation at the time of monochromatic light, that is, when the reading speed is high, and the operation at the time of multicolor light, that is, when the reading speed is low. If the gate voltage to be applied is changed between the operation at the time of monochromatic light and the operation at the time of multicolor light by the gate voltage control means of the conversion device, the sensitivity in each case can be maximized.

  In the image reading apparatus having the above-described configuration, the photoelectric conversion device may be arranged one-dimensionally, or the photoelectric conversion device may be arranged two-dimensionally.

  In the image input device, the photoelectric conversion device may be arranged one-dimensionally or two-dimensionally.

  As described above, when the photoelectric conversion device is arranged one-dimensionally, it can be suitably used for a portable image input device such as a handy scanner used in a home facsimile device.

  Further, when the photoelectric conversion device is two-dimensionally arranged, it is preferably used for a flat head scanner or the like. In this case, the entire document image can be read at once.

  Charging of the charges to the auxiliary capacitors may be performed collectively.

  In this case, there is an effect that the charging time is shortened.

  In order to solve the above problems, the two-dimensional image sensor according to the present invention is provided at each of a plurality of data lines, a plurality of scanning lines intersecting with the data lines, and an intersection of the data lines and the scanning lines. A photoelectric conversion element including a thin film transistor having a photosensitive semiconductor layer, an auxiliary capacitor connected to the drain electrode of the thin film transistor and charged with charge, and a photoelectric conversion amount detected by the thin film transistor connected to the source electrode of the thin film transistor A photoelectric conversion amount detection means, and an image information output means for outputting the result detected by the photoelectric conversion amount detection means as image information, and the auxiliary capacitor is charged with a predetermined amount of charge, and When the thin film transistor is in a non-conductive state, charge is discharged by light irradiation to the photosensitive semiconductor layer, and the photoelectric conversion amount is detected. The stage is a two-dimensional image sensor that detects the photoelectric conversion amount of the photoelectric conversion element based on the charge of the auxiliary capacitor after the light irradiation to the photosensitive semiconductor layer is completed, and sets the thin film transistor in a non-conductive state. And a gate voltage applying means for applying a gate voltage to the gate electrode of the thin film transistor when the photosensitive semiconductor layer is irradiated with light for a predetermined time, and a gate for variably controlling the gate voltage applied by the gate voltage applying means. And a voltage control means.

  According to the above configuration, it is possible to accurately read a two-dimensional image with a simple configuration.

  In the two-dimensional image sensor having the above configuration, the data line, the scanning line, the thin film transistor, and the auxiliary capacitor may be formed on a transparent substrate.

  A transparent protective layer may be formed on the surface of the transparent substrate on the side where the thin film transistor is formed.

  Further, a light irradiation means is provided on the surface of the transparent substrate opposite to the surface on which the thin film transistor is formed, and the object to be irradiated disposed on the surface on which the thin film transistor is formed is irradiated with light and reflected from the object to be irradiated. The thin film transistor may be irradiated with light.

  The light irradiation control means controls light irradiation of the light irradiation means, and the light irradiation control means performs the light irradiation for a predetermined time after the auxiliary capacitor is charged with a predetermined amount of charge. The photoelectric conversion amount detection means controls the photoelectric conversion amount by the photoelectric conversion element based on the charge of the auxiliary capacitor in a state where the light irradiation is stopped after the light irradiation by the light irradiation means for a certain time. The amount may be detected.

  In order to solve the above problems, the driving method of the two-dimensional image sensor according to the present invention drives the scanning line after a predetermined amount of charge has been charged in all the auxiliary capacitors connected to the thin film transistors. And sequentially detecting the photoelectric conversion amount by the photoelectric conversion element including the thin film transistor based on the charge of the auxiliary capacitor, and in the step, the thin film transistor is made non-conductive in the photosensitive semiconductor. When the layer is irradiated with light for a predetermined time, a gate voltage having the maximum sensitivity is applied to the gate electrode of the thin film transistor.

  According to the above configuration, it is possible to accurately read a two-dimensional image with a simple configuration.

  As described above, the photoelectric conversion device according to the present invention applies a gate voltage to the gate electrode of the thin film transistor when the thin film transistor is in a non-conducting state and the photosensitive semiconductor layer is irradiated with light for a predetermined time. By applying the application means and the gate voltage control means for variably controlling the gate voltage applied by the gate voltage application means, a gate voltage that provides maximum sensitivity is applied to the gate electrode of the thin film transistor. Therefore, there is an effect that it is possible to realize a photoelectric conversion device that can obtain a sufficient photoelectric conversion amount, that is, an optimum sensitivity.

  An embodiment of the present invention will be described as follows.

  First, a photosensor applied to the photoelectric conversion apparatus of the present invention and a two-dimensional image sensor (image reading apparatus) using the photosensor will be described, and then a photoelectric conversion amount detection method will be described.

  The photosensor basically has an inverted staggered thin film transistor (TFT) configuration (if the upper gate electrode is a light transmissive material, it may have a coplanar type thin film transistor configuration). That is, as shown in FIG. 2, the phototransistor 7 has the following configuration.

  That is, a bottom gate electrode 11 made of chromium (Cr) or the like is formed on a transparent insulating substrate (transparent substrate) 9 made of glass or the like, and covers the bottom gate electrode 11 and the insulating substrate 9. A bottom gate insulating film (protective layer) 13 made of silicon nitride (SiN) is formed.

  A semiconductor layer (photosensitive semiconductor layer) 12 made of i-type amorphous silicon (ia-Si) is formed on the bottom gate electrode 11 at a position facing the bottom gate electrode 11. A source electrode 10 and a drain electrode 15 are formed on the semiconductor layer 12 at a position facing each other with a predetermined interval across the semiconductor layer 12.

  The source electrode 10 and the drain electrode 15 are connected to the semiconductor layer 12 through the n + silicon layer 4, respectively.

  An insulating film 14 is formed on the source electrode 10 and the drain electrode 15, and a transistor (reverse staggered thin film transistor) is configured by these.

  The phototransistor 7 is irradiated with irradiation light 2 from the backlight unit 18 on the insulating substrate 9 side, and the irradiation light 2 passes through the opening 6 and is reflected by the document 1 to irradiate the silicon layer 4. Is done.

  The phototransistor 7 having the above configuration can control the conduction state and the non-conduction state by controlling the voltage applied to the bottom gate electrode 11. For example, when a positive voltage is applied to the bottom gate electrode 11 of the phototransistor 7, an n channel is formed in the semiconductor layer 12. Here, when a positive voltage is applied between the source electrode 10 and the drain electrode 15, the source electrode 10 side Electrons are supplied and current flows.

The relationship between the gate voltage and the drain current of the phototransistor 7 is as shown in the graph of FIG. A curve I1 shows the relationship between the gate voltage and the drain current at the time of light irradiation, and a curve I2 is a graph showing the relationship between the gate voltage and the drain current at the time of no light irradiation, that is, the curve I1 shown in FIG. As shown, when light is irradiated in a non-conduction state (a state where a negative voltage is applied to the bottom gate electrode 11), a photocurrent is induced in the semiconductor layer 12, and is induced between the source electrode 10 and the drain electrode 15 by irradiation light. A drain current corresponding to the number of electron holes generated, that is, the amount of irradiation light flows. Further, when no light is irradiated, the drain current is extremely small as shown by the curve I2 shown in FIG. 3, and can be, for example, about 10 ⁻¹⁴ A (ampere). As a result, the phototransistor 7 can have a large difference between the drain current (I1) when irradiated with light and the drain current (I2) when not irradiated with light. Further, by accumulating the drain current at the time of light irradiation and the drain current without light irradiation for a predetermined time, the difference can be further increased, and a photoelectric conversion device having a large dynamic range can be obtained. This dynamic range is taken as the sensitivity of the phototransistor 7.

  Next, a two-dimensional image sensor using the photoelectric conversion device having the above configuration as a photosensor will be described below with reference to FIGS.

  FIG. 4 is a block diagram showing a schematic configuration of the two-dimensional image sensor, and FIG. 5 is a perspective view showing an outline of the two-dimensional image sensor. Note that the two-dimensional image sensor described here is a contact image sensor. In this embodiment mode, a two-dimensional image sensor is described. However, the photoelectric conversion device of the present invention can be applied to a one-dimensional image sensor as a photosensor.

  As shown in FIG. 4, the two-dimensional image sensor according to the present embodiment has a plurality of pixels (not shown) arranged in a matrix and forms a sensor unit (photosensor). A substrate (photoelectric conversion element) 20 is provided, and a plurality of drive ICs 19 and a plurality of detection ICs (photoelectric conversion amount detection means) 25 are connected to the outer periphery of the sensor substrate 20.

  The drive IC 19 drives a TFT 7 (see FIG. 1), which will be described later, provided on the sensor substrate 20 for each pixel, and is connected to gate lines 22 provided on the sensor substrate 20. The number of gate lines 22... Is several hundred to several thousand lines depending on the size of the sensor substrate 20 and the pixel pitch, and these gate lines 22 are shared by a plurality of drive ICs 19. . In this case, the number of outputs of one drive IC 19 is, for example, several hundred.

  Each of these drive ICs 19 is mounted on a drive printed circuit board 21, and each drive IC 19 and the drive printed circuit board 21 constitute a drive circuit 28.

  The drive printed circuit board 21 is connected to a control / communication board (light irradiation control means) 24 and has a circuit for controlling the drive IC 19 and interfacing with the control / communication board 24.

  On the other hand, the detection IC 25 detects an output from the sensor substrate 20 obtained as a result of driving the TFT 7 provided on the sensor substrate 20. Each detection IC 25 is connected to the data lines 23 of the sensor substrate 20. The number of data lines 23 is also several hundred to several thousand lines depending on the size of the sensor substrate 20 and the pixel pitch, and the detection of the output from the data lines 23 is shared by a plurality of detection ICs 25. is doing. The number of inputs of one detection IC 25 is, for example, several hundred.

  Each of these detection ICs 25 is mounted on a detection printed circuit board (image information output means) 26, and each detection IC 25 and the detection printed circuit board 26 constitute a detection circuit (detection means) 29.

  The detection printed circuit board 26 is connected to the control / communication board 24 and has a circuit for controlling the detection IC 25 and interfacing with the control / communication board 24.

  The control / communication board 24 includes a circuit for handling signals that are not synchronized with the line readout scanning and frame period of the sensor board 20, such as a CPU and a memory. Control is performed. Details of the control / communication board 24 will be described later.

  The backlight unit 18 includes an LED, a light guide plate, and a light diffusion plate.

  The turning on / off of the LED is controlled by the control / communication board 24.

  As shown in FIG. 5, the two-dimensional image sensor having the above configuration is provided such that the drive printed board 21 and the detection printed board 26 enter the surface of the backlight unit 18 opposite to the sensor board 20. In this case, the drive IC 19 and the detection IC 25 are formed in a substantially U-shaped cross section. By adopting such a configuration, the two-dimensional image sensor is miniaturized.

  Further, in the above two-dimensional image sensor, a transparent protective film 3 is formed in a predetermined region of the sensor substrate that becomes a sensor portion, so that the surface of the sensor substrate 20 is protected.

  Here, a general operation of the photosensor having the above configuration will be described below with reference to FIG. FIG. 1 is a schematic block diagram of a photosensor corresponding to one pixel.

  As described above, the phototransistor 7 composed of the TFT shown in FIG. 2 is irradiated with the irradiation light 2 from the backlight unit 18 on the insulating substrate 9 side, and this irradiation light 2 passes through the opening 6 and the document 1 Then, the silicon layer 4 that serves as a contact layer is irradiated.

  The phototransistor 7 can control the conduction state and the non-conduction state by controlling the voltage applied to the bottom gate electrode 11. For example, when a positive voltage is applied to the bottom gate electrode 11 of the phototransistor 7, an n channel is formed in the semiconductor layer 12. Here, when a positive voltage is applied between the source electrode 10 and the drain electrode 15, the source electrode 10 side Electrons are supplied and current flows.

Further, as shown by a curve I1 in FIG. 3, a photocurrent is induced in the semiconductor layer 12 during light irradiation in a non-conduction state (a state where a negative voltage is applied to the gate electrode), and the source electrode 10 and the drain electrode 15 are connected. In addition, a drain current corresponding to the number of electron holes induced by the irradiation light, that is, the amount of irradiation light flows. Further, when no light is irradiated, the drain current is extremely small as shown by the curve I2 in FIG. 3, and can be, for example, about 10 ⁻¹⁴ A (ampere).

  As a result, the phototransistor 7 can make a large difference between the drain current (I1) when irradiated with light and the drain current (I2) when not irradiated with light.

  In addition, the auxiliary capacitor 17 is charged with a predetermined charge, and this charge is discharged for a predetermined time by the drain current when irradiated with light and the drain current when no light is irradiated, and the charge remaining in the auxiliary capacitor after emission is detected by the detection IC 25. By doing so, the difference can be made larger and a photoelectric conversion device having a large dynamic range can be obtained.

  As shown in FIG. 1, the detection IC 25 includes an integration amplifier 33, a low-pass filter 34, an amplification amplifier 35, a sample hold circuit 36, etc., for the number of lines (for example, several hundred lines) detected by the detection IC 25. Further, an analog multiplexer 37 and an A / D (analog / digital) conversion circuit 38 are provided one after the sample hold circuit 36.

  The detection IC 25 performs double correlation sampling in order to remove the offset and noise of each component circuit.

  In the detection IC 25 having such a configuration, the charge of the auxiliary capacitor 17 input to the detection IC 25 through the data line 23 is first input to the integration amplifier 33 as a negative input. A potential proportional to the generated charge is output. A reference voltage (Vref) 32 is connected to the positive input of the integrating amplifier 33.

  The output of the integration amplifier 33 is input to the amplification amplifier 35 through a low-pass filter 34 provided to reduce noise, amplified by a predetermined factor, and output.

  The output of the amplification amplifier 35 is input to the sample hold circuit 36 and temporarily held, and the held value is output to one input of a plurality of inputs of the analog multiplexer 37.

  The output of the analog multiplexer 37 is input to the A / D conversion circuit 38 in the next stage, and the A / D conversion circuit 38 converts the analog data into digital data, and outputs it to the control / communication board 24 as image data. Is done.

Further, the integration amplifier 33 is provided with a reset switch 30, and the reset switch 30 is controlled by the output of the control unit 31 of the detection IC 25. The control unit 31 controls the detection IC 25 and interfaces with the detection printed board 26.

  The phototransistor 7 having the above-described configuration is connected to the drive IC 19 through a gate line 22 connected to the gate electrode 11 (hereinafter referred to as gate G). The driving IC 19 is an IC for applying a gate voltage to the gate G, and is connected to the control / communication board 24.

  The control / communication board 24 is a board for driving and controlling the drive IC 19, and includes a voltage control section (gate voltage generation section) 101 for generating a voltage value to be applied to the gate G, and the present image reading apparatus. A reading speed switching signal generation unit 102 that generates a reading speed switching signal for switching the reading speed in the image reading mode, and a mode switching signal generation unit 103 for generating a mode switching signal for switching the reading mode in the image reading apparatus. Contains.

  The reading speed switching signal generator 102 generates the reading speed determined by the image reading apparatus (a signal indicating the result of determining whether the document is pre-scanning or main scanning) as a reading speed switching signal. Instead of the image reading apparatus determining the reading speed, the reading speed may be input from an operation panel (not shown) provided in the image reading apparatus.

  The mode switching signal generation unit 103 generates a mode determined by the image reading apparatus (a mode in which it is determined whether the document is a monochrome document or a color document) as a mode switching signal. Instead of the mode being determined by the image reading apparatus, the mode may be input from an operation panel (not shown) provided in the image reading apparatus.

  Based on the reading speed switching signal generated by the reading speed switching signal generation unit 102 and the mode switching signal generated by the mode switching signal generation unit 103, the voltage control unit 101 performs the phototransistor 7. Is generated and applied to the gate G of the phototransistor 7 through the driving IC 19.

  In this voltage control unit 101, the sensitivity of the phototransistor 7 is maximized based on the relationship between the input reading speed switching signal and mode switching signal and the gate voltage at which the sensitivity of the phototransistor 7 maximizes the reading speed and mode. A gate-gate voltage is derived. Specifically, the relationship between the reading speed and mode and the gate voltage at which the sensitivity of the phototransistor 7 is maximized is tabulated in advance, and the gate voltage is obtained from the input reading speed switching signal and the mode switching signal.

  In an example of the present embodiment, the gate voltage that maximizes the sensitivity of the phototransistor 7 is set as Vgl = High and Vgl = Low under the following two conditions from the sensitivity characteristic results shown in FIGS. did.

(1) When the reading speed is 6 frames / second: Vgl = −7 V (High)
(2) When the reading speed is 3 frames / second: Vgl = −11.5 V (Loe)
That is, the voltage control unit 101 is configured to transmit the gate voltage Vgl to the driving IC 19 by selecting High or Low as necessary.

  In FIG. 1, for convenience of explanation, it is described that the control / communication board 24 directly controls the drive IC 19, but actually, as shown in FIG. 4, the control / communication board 24 is The drive IC 19 is controlled via the drive printed board 21.

  Further, as shown in FIG. 1, the photosensor having the above configuration drives the electrode on the side opposite to the TFT drain of the auxiliary capacitor 17 with a voltage (CS electrode driving voltage 40) different from the reference voltage 32. ing. The reference voltage 32 shown in FIG. 1 is a constant voltage, and the CS electrode drive voltage 40 is a binary voltage.

  Here, the operation of the photosensor having the above configuration will be described below with reference to the timing chart of FIG.

  Next, the operation of each part of the photosensor having the above configuration will be described with time. FIG. 6 shows a time chart of each part in the photosensor. In this time chart, for the sake of convenience of explanation, it is assumed that there is no charge in the auxiliary capacitor 17 before the time t1 of the section 1.

(1) Time t1 to t5 of section 1
At time t1 in section 1, the reset switch 30 of the integration amplifier 33 is turned off and the reset of the integration amplifier 33 is released. When the gate drive signal is turned on at time t2 and the TFT 7 is turned on, a feed-through phenomenon occurs in which charge leaks from the gate to the drain D and the source S. Due to the leaked charge (holes), the output of the integrating amplifier 33 is Descend. In the TFT 7, the TFT 7 has a portion overlapping the gate G between the gate G and the drain D and between the gate G and the source S, and a parasitic capacitance exists in the overlap portion. (See FIG. 1).

  The waveform of the integrating amplifier 33 is lower than the time t1 by the value W1 after the time t2, because of the above-described feedthrough phenomenon. At this time, the output of the integrating amplifier 33 is delayed in falling due to the time constant of the data line 23 of the sensor substrate 20.

  The output of the low-pass filter 34 to which the output of the integrating amplifier 33 is input falls from the time t2 toward the output value of the integrating amplifier 33 with a time constant. This decrease eventually becomes the value W1.

  The output of the amplification amplifier 35 to which the output of the low-pass filter 34 is input falls toward the output value × G (gain) of the integration amplifier. This decrease finally becomes the value W1 × G, and this value is sampled and held at time t3. This sampled value is the parasitic capacitance of the TFT 7 and the feedthrough signal component from the auxiliary capacitance.

  Next, when the reset switch 30 of the integration amplifier 33 is turned on from time OFF at time t4, the feedback capacitor 39 of the integration amplifier 33 is short-circuited, and the output of the integration amplifier 33 becomes the reference voltage (Vref). For this reason, the outputs of the low-pass filter 34 and the amplification amplifier 35 are also Vref.

  When the CS electrode drive voltage is turned on at time t5, charges (holes) flow from the auxiliary capacitor into the drain D of the TFT 7, but the charges disappear because the integration amplifier 33 is reset.

(2) Time t6 to t7 in section 1
When the gate drive signal is turned off at time t6, charges (electrons) flow into the feedback capacitor 39 of the integrating amplifier 33 due to the feedthrough phenomenon caused mainly by the parasitic capacitance between the gate and the source S of the TFT 7, Since the amplifier 33 is in the reset state, the charge that has flowed in disappears. On the other hand, due to the feedthrough phenomenon due to the parasitic capacitance mainly between the gate and the drain D of the TFT 7, charges (electrons) flow into the auxiliary capacitance 17, and the TFT drain voltage decreases by W2.

  Next, when the CS electrode drive voltage is turned off at time t 7, charges (electrons) flow from the auxiliary capacitor 17 into the drain D of the TFT 7. Due to this charge, the output of the integrating amplifier 33 falls to the value W3.

  At this time, when the TFT 7 is irradiated with light, the charge of the auxiliary capacitor 17 flows to the source S side of the TFT 7 due to the photocurrent, and the TFT drain voltage increases accordingly (from t7 in section 1 to t2 in section 2). ). Further, since no photocurrent is generated in the TFT 7 that is not irradiated with light, the charge of the auxiliary capacitor 17 is held, and the TFT drain voltage does not change.

  Furthermore, two types of gate voltages (Vgl = High and Vgl = Low) are selectively applied to the gate G of the TFT 7 when the pixel is irradiated with light. In this case, it can be seen from FIG. 6 that the drain voltage of the TFT is higher when the gate voltage Vgl = High is applied than when the gate voltage Vgl = Low is applied.

(3) Time t1 to t4 of section 2
At time t1 in section 2, the reset switch 30 of the integration amplifier 33 is turned off and the reset of the integration amplifier 33 is released. When the gate drive signal is turned on at time t2 and the TFT 7 is turned on, a feed-through phenomenon occurs in which charge leaks from the gate to the drain D and the source S. Due to the leaked charge (holes), the output of the integrating amplifier 33 is Descend. At this time, the charges (electrons) injected into the auxiliary capacitor 17 also flow to the source S side at times t6 and t7 in section 1, and the output of the integrating amplifier 33 rises. The amount of charge at this time varies depending on the state of light irradiation to the TFT.

  FIG. 6 shows a TFT (pixel) that is completely exposed to light and a TFT that is not irradiated. Due to the difference in the amount of charge, a difference of W4 (t3) is produced between the output of the integrating amplifier of the TFT that was exposed to light and the output of the integrating amplifier of the TFT that was not exposed to light. This decrease finally becomes the value W4 × G, and this value is sampled and held at time t3. This sampled and held value is the difference between the detection value of the pixel irradiated with light and the pixel not irradiated.

  Next, when the reset switch 30 of the integration amplifier 33 is turned on from time OFF at time t4, the feedback capacitor 39 of the integration amplifier 33 is short-circuited, and the output of the integration amplifier 33 becomes the reference voltage (Vref). For this reason, the outputs of the low-pass filter 34 and the amplification amplifier 35 are also Vref.

  Subsequently, when the CS electrode drive voltage is turned on at time t5, charges (holes) flow from the auxiliary capacitor 17 to the drain of the TFT 7, but the charges disappear because the integration amplifier 33 is reset. .

(2) Time t6 to t7 in section 2
When the gate drive signal is turned off at time t6, charges (electrons) flow into the feedback capacitor 39 of the integrating amplifier 33 due to the feedthrough phenomenon caused mainly by the parasitic capacitance between the gate and the source S of the TFT 7, Since the amplifier 33 is in the reset state, the charge that has flowed in disappears. On the other hand, due to the feedthrough phenomenon due to the parasitic capacitance mainly between the gate and the drain D of the TFT 7, charges (electrons) flow into the auxiliary capacitance 17, and the TFT drain voltage decreases by W2.

  Next, when the CS electrode drive voltage is turned off at time t7, charges (electrons) flow into the drain of the TFT 7 from the auxiliary capacitor. Due to this charge, the output of the integrating amplifier 33 falls to the value W3. At this time, when the TFT 7 is irradiated with light for a predetermined time, the charge of the auxiliary capacitor 17 flows to the source side of the TFT 7 due to the photocurrent, and accordingly, the TFT drain voltage rises (from t7 in section 2). Further, since no photocurrent is generated in the TFT 7 that is not irradiated with light, the charge of the auxiliary capacitor 17 is held, and the TFT drain voltage does not change.

  As described above, the amount of photoelectric conversion can be detected once at time t3 in section 2 by performing the operation from section 1 to section 2 once. Further, by repeating the operation from the section 1 to the section 2, the above detection operation is repeated, and the photoelectric conversion amount can be continuously detected at the time t3 in the sections 1 and 2.

  Another detection operation in the two-dimensional image sensor including the photoelectric conversion device having the above configuration will be described with reference to FIGS. FIG. 7 is a flowchart showing a flow of operations of the two-dimensional image sensor.

  As shown in this figure, the operation of the two-dimensional image sensor is performed by a batch charging period (steps S1 to S4) in which a predetermined charge is charged (batch charging) in the auxiliary capacitors 17 in all pixels, and light from the backlight unit 18. Light irradiation period (step S5) and a scanning period (steps S6 to S17) for acquiring image information of each pixel.

  FIG. 8 is a timing chart showing the operation of the two-dimensional image sensor shown in FIG. FIG. 8 shows an example in which the number of lines (number of rows) scanned in one frame period is 512.

  In FIG. 8, the scan period is from time t1 to t5, the collective charge period is from time t5 to t9, and the light irradiation period is from t9 to t1 (time t1 at which scanning of the first row starts in the next frame period). Each is supposed to be done. Here, the collective charging performed at times t5 to t9 is performed in order to perform a scanning process in the next frame. In other words, it is assumed that collective charging is performed in the previous frame period before the scan processing at time t1 to t5 is performed. However, in the following description, for convenience of explanation, it is assumed that the operation starts from the collective charging period (time t6).

(1) Batch Charging Period First, at time t6 (see FIG. 8), the control / communication board 24 turns on the TFTs 7 in all the pixels. That is, based on an instruction from the control / communication board 24, the drive IC 19 turns on the gate drive signals for all the TFTs 7 (step S1 (see FIG. 7)).

  At this time, it is assumed that the reset switch 30 of the integrating amplifier 33 is on. Therefore, when the TFT 7 is turned on, a feedthrough phenomenon in which charges leak from the bottom gate electrode 11 to the drain D and the source S occurs, but the TFT drain voltage becomes the reference voltage Vref.

  Here, a method for turning on all the gate drive signals will be described below. FIG. 9 shows a schematic circuit diagram of a gate driver mounted on the driving IC 19. This figure shows the case of a 256 output configuration. However, when more gates (gate lines) are driven, a plurality of gate drivers may be driven in cascade connection.

  The gate driver shown in FIG. 9 includes a shift register 51 including a plurality of cascaded D-TYPE flip-flops and the same number of AND gates 52 as the flip-flops. Although the shift register 51 in FIG. 9 uses a D-TYPE flip-flop, the present invention is not limited to this, and other types of flip-flops may be used.

  The OE terminal (low active) controls the output of the gate driver outputs (OG1 to OG256). When the OE terminal is high, all outputs are kept at a low level. The output enable signal from the OE terminal is input to one input terminal of each AND gate 52, and the output signal from the output terminal Q of each stage flip-flop in the shift register 51 is the other input terminal of the corresponding AND gate 52. Is input.

  FIGS. 10A and 10B are timing charts for explaining a method of simultaneously turning on all output lines by the gate driver shown in FIG. 9, and shows two methods (method A and method). B).

  The method A shown in FIG. 10A is a method of driving all outputs simultaneously by inputting a start pulse (STPL) and a shift clock (CLOCK).

  In the method A, the outputs (OG1i to OG256i) of all the shift registers 51 are turned on in the periods ta1 to ta4. Then, during the period ta2 to ta3, the OE terminal is set to low, so that the outputs (OG1i to OG256i) of the shift register 51 are output to the output terminals (OG1 to OG256). In this method, the PRESET terminal and the CLEAR terminal of the flip-flop of FIG. 9 are not necessary, and the circuit configuration of the shift register 51 is simplified.

  In the method B shown in FIG. 10B, the outputs (OG1i to OG256i) of the shift register 51 are turned on in the periods tb1 to tb4 by turning on the PRESET terminal of the shift register 51. Then, when the OE terminal is set to low in the period tb2 to tb3, the outputs (OG1i to OG256i) of the shift register 51 are output to the output terminals (OG1 to OG256). In this method, since there is no control by CLOCK, the time required to turn on all the gate drive signals can be shortened compared to method A.

  All of the gate drive signals can be turned on by either method A or method B.

  Next, at time t7, the control / communication board 24 turns on the CS electrode drive voltage (Vcs) (turns on the CS electrode drive signal) (step S2). As a result, charges (holes) flow from the auxiliary capacitor 17 to the drain of the TFT 7, but since the integrating amplifier 33 is reset, this charge disappears.

Next, at time t8, the control / communication board 24 turns off the TFTs 7 in all the pixels. That is, based on an instruction from the control / communication board 24, the drive IC 19 turns off the gate drive signals for all the TFTs 7 (step S3). As a result, the charge (electrons) flows into the feedback capacitor 39 of the integration amplifier 33 due to the feedthrough phenomenon caused mainly by the parasitic capacitance between the gate and the source S of the TFT 7, but the integration amplifier 33 flows in because of the reset state. The incoming charge disappears.
Further, charge (electrons) flows into the auxiliary capacitor 17 mainly due to a feedthrough phenomenon due to the parasitic capacitance between the gate and the drain D of the TFT 7. As a result, the TFT drain voltage drops by W1.

  Next, at time t9, the control / communication board 24 turns off the CS electrode drive voltage (V0) (turns off the CS electrode drive signal) (step S4). When the CS electrode drive voltage Vcs is turned off, the TFT drain voltage is turned off and non-conducting. Therefore, only the amount corresponding to the difference between the on-off voltage of the CS electrode drive voltage 40 (value W2). Descend. As a result, a predetermined amount of charge is charged (collectively charged) into the auxiliary capacitors 17 in all the pixels.

(2) Light Irradiation Period Next, the control / communication board 24 controls the backlight unit 18 to irradiate light from time t9 to time t1 when scanning of the first gate line is started in the next frame period. (Step S5). As described above, the light emitted from the backlight unit 18 is applied to the document through the opening 6 in the sensor substrate 20. Then, the light reflected by the original is applied to the TFT 7. As a result, with the TFT 7 turned off, the TFT 7 is irradiated with the reflected light from the document for a predetermined period.

  As a result, in the TFT 7 irradiated with the light reflected by the original, a photocurrent flows between the source and drain electrodes. As a result, the charge of the auxiliary capacitor 17 flows to the source side of the TFT 7, and the TFT drain voltage rises accordingly.

  On the other hand, since no photocurrent is generated in the TFT 7 that is not irradiated with light, the charge amount of the auxiliary capacitor 17 is maintained and the TFT drain voltage does not change.

(3) Scan period Next, the process proceeds to a scan period in which image information of each pixel is acquired. The scan process is sequentially performed for each line. That is, the same scanning process is sequentially performed from the first line to the last line (for example, 512 lines).

  First, at time t1, the control / communication board 24 switches the reset switch 30 of the integration amplifier 33 of each pixel in the scanning line from on to off, and releases the reset of the integration amplifier 33 (step S6).

  Next, at time t2, the control / communication board 24 controls the drive IC 19 to turn on the gate drive signal of each pixel in the line to be scanned (step S7). That is, the TFT 7 that performs scanning is turned on.

  Here, when the gate drive signal is turned on and the TFT 7 is turned on, a feedthrough phenomenon in which charges leak from the gate G to the drain D and the source S occurs, and charges (holes) leak. At this time, the charge (electrons) injected into the auxiliary capacitor 17 also flows to the source S side, and the output of the integrating amplifier 33 rises.

  At this time, the amount of charge flowing to the source S side varies depending on the state of light irradiation to the TFT 7. That is, since the TFT 7 is a light detection element whose resistance value changes according to the amount of light applied, the TFT 7 (pixel) that receives the reflected light from the original and the TFT 7 (pixel) that does not receive the reflected light from the original. The amount of charge flowing to the source S side is different. Further, the electric charge that has flowed to the source S side in this way is input to the negative input of the integrating amplifier 33.

  Next, at time t3, a voltage proportional to the input charge amount is output from the integrating amplifier 33 (step S8).

  It should be noted that in the case of the TFT 7 that is completely exposed to light and the TFT 7 that is not exposed to light, the voltage of the TFT drain (drain D of the TFT 7), the output of the integrating amplifier 33, the output of the low pass filter 34, and the output of the amplification amplifier 35 in FIG. Is shown. Then, as shown in FIG. 8, there is a difference of W3 at time t3 between the output of the integrating amplifier 33 of the TFT 7 to which the light hits and the output of the integrating amplifier 33 of the TFT 7 to which no light hits.

  At time t3, the value (signal) output from the integrating amplifier 33 is input to the amplification amplifier 35 via the low-pass filter 34, multiplied by a predetermined gain g, and amplified (step S9). That is, in the amplification amplifier 35, an output of W3 × g is obtained by multiplying the difference W3 by the gain g. The difference in the amount of charge after amplification is the difference between the detection values of the pixel irradiated with light and the pixel not irradiated.

  At time t3, the value amplified by the amplification amplifier 35 is sent to the sample hold circuit 36 and temporarily held (sample hold) (step S10).

  Next, at time t4, the control / communication board 24 switches the reset switch 30 of the integrating amplifier 33 from OFF to ON (step S11). As a result, the feedback capacitor 39 of the integrating amplifier 33 is short-circuited, and the output of the integrating amplifier 33 becomes the reference voltage Vref. Therefore, the outputs of the low-pass filter 34 and the amplification amplifier 35 are also the reference voltage Vref.

  Next, at time t5, the control / communication board 24 controls the drive IC 19 to turn off the gate drive signal and turn off the TFT 7 (step S12). As a result, the charge (electrons) flows into the feedback capacitor 39 of the integration amplifier 33 due to the feedthrough phenomenon caused mainly by the parasitic capacitance between the gate G and the source S of the TFT 7, but the integration amplifier 33 flows in because it is in the reset state. The charge that came in disappears. On the other hand, due to the feedthrough phenomenon due to the parasitic capacitance mainly between the gate G and the drain D of the TFT 7, charges (electrons) flow into the auxiliary capacitance 17 and the TFT drain voltage decreases by W1.

Next, the control / communication board 24 determines whether or not the processes in steps S6 to S12 have been performed on all lines (step S13).
And when the line which has not performed said process remains, the process of step S6-S12 is performed with respect to the remaining line.

  On the other hand, when the processing of S6 to S12 is completed for all the lines, the control / communication board 24 outputs the value sampled and held by the sample and hold circuit 36 to each of the plurality of inputs of the analog multiplexer 37. (Step S14).

  The value input to the analog multiplexer 37 is output to the A / D conversion circuit 38, where the analog data is converted to digital data by the A / D conversion circuit 38 to obtain image data (step S15).

  The image data generated by the A / D conversion circuit 38 is output to the control / communication board 24 via the control unit 31 and the detection printed board 26 (step S16).

  Next, the control / communication board 24 determines whether or not all frames have been scanned (step S17). If a frame that has not been scanned remains, the process from step S1 is performed on the next frame. On the other hand, when all the frames have been scanned, the control / communication board 24 ends the operation.

  As described above, the photoelectric conversion amount in each pixel can be detected once by performing the collective charging period, the light irradiation period, and the scanning period once (one cycle). In addition, by repeating a cycle including a batch charging period, a light irradiation period, and a scanning period, it is possible to continuously detect the photoelectric conversion amount in each pixel at time t3 in the scanning period of each cycle.

In the two-dimensional image sensor, the TFT 7 has a photo sensor function and a pixel selection function.
As a result, the photosensor portion (sensor substrate 20) can be made smaller, the pixels can be densified, and a photosensor with a simple structure can be realized.

  In the two-dimensional image sensor, the auxiliary capacitor 17 is filled with a predetermined amount of charge, and the charge charged in the auxiliary capacitor 17 is accumulated in the auxiliary capacitor 17 after flowing out as a photocurrent for a predetermined time. A charge amount obtained by subtracting the charges is detected as a photoelectric conversion amount.

  Therefore, it is possible to realize a photoelectric conversion device having a large dynamic range as compared with the case where the photocurrent itself generated at the time of light irradiation is detected.

  Further, in the two-dimensional image sensor, it is possible to charge a predetermined amount of charge to the auxiliary capacitor 17 at once by using the CS electrode driving voltage Vcs.

  As a result, a complicated structure is not required, the auxiliary capacitor 17 can be charged (charged) in each pixel with simple timing control, and a photosensor with a large dynamic range can be realized.

  Also here, as described above, two types of gate voltages (Vgl = High and Vgl = Low) are selectively applied to the gate G of the TFT 7 when the pixel is irradiated with light. . In this case, it can be seen from FIG. 8 that the drain voltage of the TFT is higher when the gate voltage Vgl = High is applied than when the gate voltage Vgl = Low is applied.

  Here, another operation of the photosensor configured as described above will be described below with reference to the timing chart of FIG. The timing chart shown in FIG. 11 is almost the same as the timing chart shown in FIG. 6 described above, but the polarities of the output of the integrating amplifier, the output of the low-pass filter, and the output of the amplification amplifier in the section (2) are reversed. Is different.

  That is, FIG. 11 shows the time chart of each part in this apparatus by the waveforms AH. Here, in this time chart, in order to explain that the photoelectric conversion amount can be obtained by a simple and repetitive method, and in order to explain the connection between the operation and the operation in an easy-to-understand manner, the two operations will be described separately in sections.

In this time chart, for convenience of explanation, it is assumed that there is no charge in the auxiliary capacitor 17 before the time t1 of the section 1, the CS electrode drive voltage of the waveform D is V2, and the drain voltage of the TFT 7 of the waveform E is Vref. ing.
(1) Time t1 to t3 in section 1
As shown in the waveform B, the reset switch 30 of the integration amplifier 33 is turned off from the on state at time t1 in the section 1, and the reset of the integration amplifier 33 is released.

  As shown in the waveform C, when the gate drive signal is turned on at time t2 and the TFT 7 is turned on, a feedthrough phenomenon occurs in which charge leaks from the gate to the drain D and source S, and the leaked charge (holes) causes As shown by the waveform F, the output of the integrating amplifier 33 falls. In the TFT 7, the TFT 7 has a portion overlapping the gate (see FIG. 4) between the gate and the drain D and between the gate and the source S, and the parasitic capacitance 41 exists in the overlapping portion. It happens because you are.

  As indicated by the waveform F, the output of the integrating amplifier 33 is lower by the value W1 than at time t1 at time t3 because of the effect of the feedthrough phenomenon. At this time, the output of the integrating amplifier 33 is delayed in falling due to the time constant of the data line 23 of the sensor substrate 20.

  As shown by the waveform G, the output of the low-pass filter 34 to which the output of the integration amplifier 33 is input falls from the time t2 toward the output value of the integration amplifier 33 with a time constant. This descending width finally becomes the value W1.

  As shown by the waveform H, the output of the amplification amplifier 35 to which the output of the low-pass filter 34 is input decreases toward the output value of the integrating amplifier 33 × G (gain). This descending width finally becomes the value W1 × G, and this value is sampled and held at time t3 (pulse output timing in the sample hold signal shown in waveform A). This value W1 × G is a feedthrough signal component. The reason why the sample-and-hold is also performed in the section 1 in this way is that it is assumed that the circuit operates at the same timing as the section 2 described later.

  As shown in the waveform D, the CS electrode drive voltage 40 takes a binary voltage (V2, V3) in this embodiment, but takes a value V2 from t1 to t3. The relationship between V2 and V3 is V2> V3. These V2 and V3 are connected to the drain D of the TFT 7 by capacitive coupling of the auxiliary capacitor 17, and when the CS electrode drive voltage is lowered from V2 to V3 as shown at time t6 of the waveform D when the TFT 7 is turned off. As shown at time t6 to t1 of the waveform E, the TFT drain voltage is also relatively lowered by the potential difference (W3) of V2-V3.

  Note that the magnitude relationship between Vref and V2 and V3 is not necessarily V2> Vref> V3. This is because this is capacitive coupling by a capacitor, that is, the potential difference of Vref is created by the potential difference between V2 and V3, and the magnitude relationship is determined by the amount of charge to the auxiliary capacitor, the operating voltage of the LSI, and the like.

(2) Time t4 to t6 in section 1
As shown in the waveform B, when the reset switch 30 of the integration amplifier 33 is turned on from the OFF at the time t4 in the interval 1, the feedback capacitor 39 of the integration amplifier 33 is short-circuited, and the output of the integration amplifier 33 is shown in the waveform F. Becomes the reference voltage (Vref). For this reason, as shown in the waveform G and the waveform H, the outputs of the low-pass filter 34 and the amplification amplifier 35 are also Vref. Note that, as shown by the waveform E, the drain voltage of the TFT 7 also maintains Vref.

  Further, before the time t4, the integration amplifier 33 pulls all of the charge to the feedback capacitor 39 by its action (virtual short circuit) while the gate drive signal is on, so that the charge is released from the auxiliary capacitor 17. The state (charge is 0 with respect to the voltage vref). Therefore, the integrating amplifier 33 and the feedback capacitor 39 function as an opening unit that releases the charge of the auxiliary capacitor 17 before the light irradiation. The reason why the drain voltage of the TFT 7 is Vref as described above is that all the charges generated on the drain side of the TFT 7 move to the feedback capacitor 39 of the integrating amplifier 33.

  The integrating amplifier 33 operates so as to pull the charge on the input terminal to the feedback capacitor 39 regardless of whether the reset switch 30 is on or off. However, in order to reduce the charge of the feedback capacitor 39 to 0, the reset switch 30 is turned on.

  For convenience of explanation, it is assumed that there is no charge in the auxiliary capacitor 17 before the time t1 of the section 1. However, as described above, even if there is a charge in the auxiliary capacitor 17, the gate drive signal is turned on. In this state, the charge of the auxiliary capacitor 17 can be reduced to zero by turning the reset switch 30 from OFF to ON at time t4.

  As shown in the waveform C, when the gate drive signal of the TFT 7 is turned off at time t5, the charge (electrons) is converted into an integrating amplifier due to the feedthrough phenomenon due to the parasitic capacitance 41 mainly between the gate and the source S of the TFT 7. However, since the integrating amplifier 33 is in the reset state (ON state) as shown in the waveform B, the electric charge that has flowed in disappears. On the other hand, charge (electrons) flows into the auxiliary capacitor 17 due to the feedthrough phenomenon caused mainly by the parasitic capacitance 41 between the gate and the drain D of the TFT 7, and the drain voltage of the TFT 7 is Move down by W2. Further, since the gate drive signal is in the off state, the charge of the auxiliary capacitor 17 is not pulled by the integrating amplifier 33.

  Next, as shown in the waveform D, when the CS electrode drive voltage 40 is stepped down from V2 to V3 at time t6, the potential of the drain D decreases accordingly.

  At time t6, when the TFT 2 is irradiated with the light 2 from the backlight unit 18 for a predetermined time, a charge flows from the source S side of the TFT 7 to the auxiliary capacitor 17 due to the photocurrent, and the charge is accumulated in the auxiliary capacitor 17. Along with this, the drain voltage of the TFT 7 increases (from t6 in section 1 to t1 in section 2 (broken line in waveform E)). Further, in the TFT 7 that is not irradiated with the light 2, no photocurrent is generated, so that no charge flows into the auxiliary capacitor 17 and the drain voltage of the TFT 7 does not change (from t 6 in section 1 to t 1 in section 2 (solid line of waveform E)). .

  The charge of the auxiliary capacitor 17 by the photocurrent described above is performed by changing the voltage on the drain side of the TFT 7 from Vref, and by the voltage difference generated between the source S and the drain D of the TFT 7, the OFF resistance when the TFT 7 receives light. Through this, the auxiliary capacitor 17 is charged with electric charges.

  When the potential difference between V2 and V3 is increased, the potential difference between the drain D and the source S of the TFT 7 is also increased, and the amount of charge flowing through the TFT 7 can be increased when the light 2 is irradiated. Thereby, the difference in charging amount (charging difference) between the pixel irradiated with the light 2 and the pixel not irradiated with the light 2 can be further increased. Furthermore, by increasing the potential difference of V2-V3, it is possible to shorten the irradiation time of the light 2 required to make a certain amount of charge difference between the pixel not irradiated with the light 2 and the pixel irradiated with the light 2. I can do it.

  Also here, as described above, two types of gate voltages (Vgl = High and Vgl = Low) are selectively applied to the gate G of the TFT 7 when the pixel is irradiated with light. . In this case, FIG. 11 shows that the drain voltage of the TFT is higher when the gate voltage Vgl = High is applied than when the gate voltage Vgl = Low is applied.

(3) Time t1 to t3 of section 2
As shown in the waveform B, the reset switch 30 of the integration amplifier 33 is turned off from on at time t1 in the interval 2, and the reset of the integration amplifier 33 is released in preparation for pulling the charge accumulated in the auxiliary capacitor 17 to the feedback capacitor 39. Is done. Further, when the CS electrode drive voltage is boosted from V3 to V2, the voltage of the auxiliary capacitor 17 increases by the value W3.

  Further, as shown in the waveform C, when the gate drive signal is turned on at time t2 and the TFT 7 is turned on, a feedthrough phenomenon in which charges leak from the gate to the drain D and source S occurs, and the leaked charges (holes) ), The output of the integrating amplifier 33 drops as shown by the waveform F. At this time, the charge (electrons) injected into the auxiliary capacitor 17 at time t5 in section 1 and from t6 in section 1 to t1 in section 2 also flows to the source S side and is pulled and accumulated in the feedback capacitor 39.

  At this time t2, the drain voltage of the TFT 7 becomes Vref, and the charge of the auxiliary capacitor 17 is released in preparation for the next light irradiation. In other words, the integration amplifier 33 pulls all the charges (electrons) accumulated in the auxiliary capacitor 17 to the feedback capacitor 39 so that the drain voltage of the TFT 7 becomes Vref.

  Here, as indicated by the waveform F at times t2 to t5, the output decrease width of the integrating amplifier 33 is different between the TFT 7 (pixel) to which the light 2 hits and the TFT 7 (pixel) to which the light 2 does not hit. This is because the amount of charge injected into the auxiliary capacitor 17 at time t5 in section 1 and from t6 in section 1 to t1 in section 2 varies depending on the state of irradiation of the light 2 onto the TFT 7.

  Specifically, in the case of the TFT 7 that is not exposed to light 2, only charges (electrons at t5 and holes at t2) due to the feedthrough phenomenon are pulled and accumulated in the feedback capacitor 39, whereas In the case of the TFT 7 that is exposed to light 2, the charge due to the feedthrough phenomenon (electrons at t 5 and holes at t 2) and the charges (holes) injected into the auxiliary capacitor 17 by the photocurrent are added together and returned. A difference occurs in the amount of charge accumulated in the capacitor 39.

  As a result, the output of the integrating amplifier 33 slightly decreases from Vref, as shown by the solid line at time t2 to t5 of the waveform F, indicating the output of the integrating amplifier 33 connected to the TFT 7 that does not receive light 2. As indicated by the broken line, the output of the integrating amplifier 33 connected to the TFT 7 to which the light 2 hits is further lowered by W4. That is, there is a difference of W4 (t3) between the output of the integrating amplifier 33 of the TFT 7 that was exposed to the light 2 and the output of the integrating amplifier 33 of the TFT 7 that was not exposed to the light 2.

  Since the integrating amplifier 33 is an inverting amplifier circuit, the waveform E of the higher drain voltage of the TFT 7 from t6 to t1 (broken line) is the waveform of the lower output (broken line) of the output of the integrating amplifier 33 from t2 to t5. F.

  As shown in the waveform H, this fall finally becomes the value W4 × G as the output of the amplification amplifier 35, and this value becomes the sample hold circuit at time t3 (pulse output timing in the sample hold signal shown in the waveform A). The sample is held by 36 (photoelectric conversion amount detecting means). This sampled and held value is the difference between the detection values of the pixel irradiated with the light 2 and the pixel not irradiated with the light 2. This value is output as a photoelectric conversion amount via the analog multiplexer 37, the A / D conversion circuit 38, and the control unit 31.

  Also here, as described above, two types of gate voltages (Vgl = High and Vgl = Low) are selectively applied to the gate G of the TFT 7 when the pixel is irradiated with light. . In this case, FIG. 11 shows that the drain voltage of the TFT is higher when the gate voltage Vgl = High is applied than when the gate voltage Vgl = Low is applied.

(4) Time t4 to t5 of section 2
As shown in the waveform B, when the reset switch 30 of the integrating amplifier 33 is turned on from OFF at time t4 in the interval 2, the feedback capacitor 39 of the integrating amplifier 33 is short-circuited, and the feedback capacitor 39 of the integrating capacitor 33 is ready for the next light irradiation. Charge is reduced to zero. Along with this, the output of the integrating amplifier 33 returns to the reference voltage (Vref). For this reason, as shown by the waveform G and the waveform H, the outputs of the low-pass filter 34 and the amplification amplifier 35 are also restored to Vref.

  Next, as shown in the waveform C, when the gate drive signal is turned off at time t5, the charge (electrons) is integrated due to the feedthrough phenomenon due to the parasitic capacitance 41 mainly between the gate and the source S of the TFT 7. Although it flows into the feedback capacitor 39 of the amplifier 33, since the integrating amplifier 33 is in a reset state, the charge that has flowed in disappears.

  On the other hand, charge (electrons) flows into the auxiliary capacitor 17 due to the feedthrough phenomenon caused mainly by the parasitic capacitance 41 between the gate and the drain D of the TFT 7, and as shown in the waveform E, the TFT drain voltage is Move down by W2. Next, as shown in the waveform D, when the CS electrode drive voltage is stepped down from V2 to V3 at time t6, the potential of the drain D is lowered along with the whole of W3.

  In this way, at time t6 when the charge release of the auxiliary capacitor 17 and the reset of the feedback capacitor 39 are completed, when the TFT 2 is irradiated with the light 2 for a predetermined time, the auxiliary capacitor 17 is caused to be brought into the source S side of the TFT 7 by photocurrent. As a result, charge flows, and the drain voltage of the TFT 7 increases accordingly (from t6 in section 2 (broken line in waveform E)). In addition, since no photocurrent is generated in the TFT 7 not irradiated with light, no charge flows into the auxiliary capacitor 17 and the drain voltage of the TFT 7 does not change (from t6 in section 2 (solid line of waveform E)).

  As described above, by performing the operation from the section 1 to the section 2 once, the photoelectric conversion amount can be detected once at the time t3 of the section 2. Further, in actual driving, the above-described detection operation is repeated by repeating the operations in the sections 2 to 2, and the photoelectric conversion amount can be continuously detected at the time t3.

  In the image reading apparatus using the photosensor having the above-described configuration, the color of the document, that is, whether it is monochrome or color is not specifically described. However, in the following, the document is color or monochrome. Control for maximizing the sensitivity of the sensor in each case (color mode, monochrome mode) will be described.

  Here, a case where the photosensor having the above configuration is applied to a composite image reading apparatus will be described. That is, the two-dimensional image sensor (this sensor) according to the present embodiment captures an image of a manuscript (newspaper, magazine, noun, photograph, barcode, two-dimensional code (QR code (Quick Response code), etc.)). Thus, it is a small (handy type) image sensor (image reading device) that outputs digital image data to an external information processing device.

In this sensor, a portion to be read of a document is brought into close contact with the surface of a sensor substrate (two-dimensional light detection array). Then, the light of the backlight disposed on the back surface of the sensor substrate is irradiated onto the document, and the reflected light is received by light receiving pixels formed in a matrix on the sensor substrate.
At this time, each light receiving pixel of the sensor substrate receives reflected light from a minute portion (a portion facing each light receiving pixel) in the document image, and generates image data (pixel data) corresponding to the minute portion.

In this sensor, the pixel data generated by each light receiving pixel is processed (collected) so as to obtain image data (original image data; electronic image data) of all original portions in close contact with the sensor substrate. It has become.
That is, this sensor is a contact type two-dimensional image sensor (area sensor) of a type that reads an image of a document two-dimensionally, does not require mechanical scanning, is small, thin, lightweight, and is resistant to vibration.

  FIG. 12 is a block diagram showing the configuration of this sensor. As shown in this figure, this sensor includes a backlight unit 111, an LED control unit 112, a sensor unit (sensor substrate) 113, a sensor control unit 114, a signal processing unit 115, an external interface (external I / F) 116, and a CPU 117. It is the structure provided with.

  Here, the backlight unit 111 corresponds to the backlight unit 18 shown in FIG. 1, and the sensor unit 113 corresponds to the sensor substrate 20 shown in FIG. The LED control unit 112, the external I / F 116, and the CPU 117 correspond to the control / communication board 24 shown in FIG. 4, and the signal processing unit 115 corresponds to the detection IC 25 and the detection printed board 26 shown in FIG. The control unit 114 corresponds to the drive IC 19 and the drive printed circuit board 21 shown in FIG. 4, the sensor unit 113 corresponds to the sensor board 20 shown in FIG. 4, and the backlight unit 111 corresponds to the backlight unit 18 shown in FIG. It corresponds to.

  The backlight unit (illumination unit) 111 includes three types of LEDs that generate light of three colors (red, green, and blue), and is a backlight substrate that irradiates a document with the light of these three colors.

  The sensor unit (image data generation unit, photodetection array) 113 is a flat sensor substrate (two-dimensional photodetection array) having a plurality of light receiving pixels arranged in a matrix.

  FIG. 13 is a cross-sectional view illustrating the configuration of the backlight unit 111 and the sensor unit 113.

  As shown in this figure, the backlight unit 111 and the sensor unit 113 are stacked on each other. The backlight unit 111 includes a light guide 124, a light scattering plate 122, a condensing lens sheet 121, and an LED 123.

  The LED (illuminating unit, light emitting element) 123 is a light-emitting diode (light-emitting) including three types of LEDs that irradiates the light guide 124 with red (R), green (G), and blue (B) light. diode).

  The light guide 124 allows the light of the LED 123 to enter from the side surface and exit from the surface (surface on the light scattering plate 22 side) as planar light.

  The light scattering plate 122 scatters the light emitted from the light guide 124 to achieve luminance uniformity. The condensing lens sheet 121 adjusts the path of light with uniform luminance that has passed through the light scattering plate 122 toward the sensor unit 113. The condenser lens sheet 121 and the light scattering plate 122 may be provided as necessary.

  Further, as shown in FIG. 13, the sensor unit 113 has a photosensor group (light receiving unit) 132 formed on a transparent substrate 131.

  The transparent substrate 131 is a transparent insulating substrate made of glass or quartz.

  The photosensor group 132 is a group of photosensors serving as light receiving pixels of this sensor arranged on a transparent substrate 131 in a matrix.

  The LED control unit (illumination unit) 112 illustrated in FIG. 12 is a drive circuit for independently driving (ON / OFF) the three types of LEDs of the backlight unit 111.

  The sensor control unit (image data generation unit, light receiving unit) 114 is a circuit for driving (power supply or the like) each photosensor 133 in the sensor unit 113.

  The signal processing unit (image data generation unit, control unit) 115 acquires pixel data from each phototransistor (not shown) of the sensor unit 113.

  Further, the external I / F 116 is an interface that controls communication (transmission of document image data, reception of instruction input from a PC user) with a personal computer (PC) connected to the sensor.

  The CPU (image data generation unit, control unit) 117 is a central part of the sensor that controls all the operations of the sensor.

  That is, the CPU 117 controls the LED control unit 112, the sensor control unit 114, and the signal processing unit 115 to acquire pixel data corresponding to all minute portions of the document image. The pixel data is processed to generate one image data corresponding to the entire image that is in close contact with the sensor unit 113.

  Here, an image reading process (original image data generating operation) by the CPU 117 will be described.

  First, the user brings the sensor unit 113 of the present sensor into close contact with the portion of the document to be read. Then, the user inputs an image reading instruction to the PC connected to the sensor.

  When receiving an image reading instruction input via the PC, the CPU 117 controls the LED control unit 112 to irradiate irradiation light from the backlight unit 111 toward the document.

  This irradiation light passes through the transparent substrate 131 and the opening of each photosensor 133 in the sensor unit 113, is reflected by the original (a minute portion of the original), and is applied to the phototransistor. Note that the amount of light reflected from the document is determined according to the reflectance (that is, the color) of the minute portion irradiated with light.

  In addition, the CPU 117 controls the sensor control unit 114 to keep the phototransistor active.

  As a result, a drain current corresponding to the amount of light emitted from the document P flows through the phototransistor. Further, a predetermined charge is precharged in advance to the auxiliary capacitor connected to the phototransistor. Accordingly, an amount of charge corresponding to the amount of drain current flows out from the auxiliary capacitor.

  Then, the signal processing unit 115 generates a voltage signal based on the amount of charge flowing out from the auxiliary capacitance of each photosensor 133 using a charge amplifier (not shown) or the like under the control of the CPU 117.

  Further, the signal processing unit 115 converts the generated voltage signal into a digital signal using an analog-digital converter. This digital signal becomes pixel data corresponding to a minute portion in the document P (document image) (corresponding to each light receiving pixel (photosensor 133)).

  Thereafter, the CPU 117 generates digital image data (original image data) corresponding to all original images in close contact with the backlight unit 111 based on these pixel data.

  In order to obtain color document image data, the CPU 117 sequentially irradiates light (red, green, and blue) from the backlight unit 111 toward the document P (each independently). Then, the three original image data read by the respective lights are combined to generate color original image data.

  On the other hand, monochrome document image data can be obtained by using one type of monochromatic light (either red, green, or blue).

  Next, image reading processing (composite image reading processing) including temporary reading, which is a characteristic image reading method of the present sensor, will be described.

  In this temporary reading (temporary reading process), monochrome original image data is generated, and using this data, it is tested whether or not the sensor unit 113 is in close contact with the portion (desired portion) of the original image to be read. This is a process for performing (confirming) (a process for aligning the sensor unit 113).

  In the composite image reading process, color original image data is generated (main reading) after alignment by provisional reading.

  FIG. 14 is a flowchart showing the flow of the composite image reading process by the CPU 117.

  As shown in this figure, in the composite image reading process, the CPU 117 uses the monochrome (for example, green) LED in the LED 123 to convert the original image data corresponding to the original image in close contact with the backlight unit 111 into monochrome. Generate (step S21; provisional reading).

  Then, the CPU 117 transmits monochrome document image data to the PC via the external I / F 116. The PC displays monochrome document image data to the user using a display screen (not shown).

  Then, based on the display of monochrome document image data, the user determines whether or not a desired portion of the document has been read by the sensor unit 113 (step S22). When it is determined that reading has not been performed (when it is determined that the position of the sensor unit 113 is poor), the user changes the position of the sensor unit 113 on the document.

  Further, the CPU 117 generates monochrome document image data at a predetermined cycle (for example, subframe cycle; approximately 0.2 second interval) and continues to send it to the PC. Then, the PC displays the received document image data one after another on the screen.

  Then, the user appropriately moves the sensor unit 113 and confirms document image data on the display screen that changes every moment according to the movement of the sensor unit 113.

  Here, when it is determined that a desired portion of the document can be read (when it is determined that the position of the sensor unit 113 is appropriate), the user instructs the PC to generate color document image data.

  In response to this, the PC transmits a color mode signal to the CPU 117 of this sensor. Receiving the color mode signal, the CPU 117 sequentially turns on the three color LEDs in the LED 123 to generate color color document image data (step S23). The time required for generating color original image data is about 1 second.

  FIG. 15 is a timing chart showing the color mode signal and the operation of this sensor.

  As shown in this figure, until the color mode signal is received (until the color mode signal becomes high), the CPU 117 periodically lights up the green LED (G lighting). Then, the CPU 117 controls the signal processing unit 115 to generate green monochrome document image data each time the green LED is lit, and transmit it to the PC (image generation (image reading)). Here, until the color mode signal is received, the reading speed is in the high speed mode, and after receiving the color mode signal, the reading speed is in the low speed mode. Here, the high speed mode is the above-described reading speed of 6 frames / second, and the low speed mode is the above-described reading speed of 3 frames / second. The reading speed is not limited to these.

  Thereafter, the PC sequentially displays the transmitted images.

  Further, the CPU 117 initializes the charge of the auxiliary capacitor in the light receiving pixel (photosensor) of the sensor unit 113 before the green LED is turned on (set to a precharge state (saturated state)).

  On the other hand, when the color mode signal is received, the CPU 117 sequentially turns on the red LED, the green LED, and the blue LED (R lighting, G lighting, B lighting). The above initialization is performed during lighting of each LED. Then, the CPU 117 generates document image data corresponding to each color, combines them, and transmits them to the PC. Then, the PC displays the received color original image data on the display screen.

  Further, as shown in FIG. 14, the user who has received the display of the color original image data has read the desired portion of the original image by the sensor unit 113 (whether the sensor unit 113 is in close contact with the desired portion). Whether or not) is reconfirmed at this time (step S24).

  If it is determined that the arrangement of the sensor unit 113 is poor, the user instructs the PC to perform temporary reading again. In response to this instruction, the PC stops the transmission of the color mode signal (the color mode signal is set to low), and sends a provisional reading instruction to the CPU 117.

  In response to this, the CPU 117 returns the process to step S1, and again generates monochrome document image data using the green LED.

  On the other hand, if it is determined in step S24 that the position of the sensor unit 113 is appropriate, it is determined whether or not to save a color image (step S25). If the user wants to save the read color original image data, the user instructs the PC to save the color original image data. In response to this, the PC stores the document image data (step S26), and transmits an instruction to end reading to the CPU 117 of the sensor. In response to this, the CPU 117 ends the composite image reading process.

  On the other hand, when the storage is unnecessary, the user instructs the PC to that effect. In response to this, the PC transmits an instruction to end reading to the CPU 117 of the sensor in the same manner as described above.

  As described above, in this sensor, the CPU 117 generates document image data (monochrome (monochrome) document image data) corresponding to the monochrome (green) light emitted from the backlight unit 111 and displays it to the user. Temporary reading (temporary reading process) is performed.

  In the present sensor, after such a provisional reading process, based on a user instruction, the CPU 117 generates original image data (multi-color original image data) corresponding to a plurality of colors of light (main reading). Process).

  That is, in this sensor, in the provisional reading step, single-color (green) document image data is generated, and thereby the reading state (position of the sensor unit 113) is tested. Therefore, power consumption and time relating to generation of document image data can be reduced as compared with a configuration in which color (multicolor) document image data is generated in the provisional reading process. For this reason, the provisional reading process can be performed in a short time.

  Further, since the resolution and resolution are not reduced in the provisional reading step, the reading state can be confirmed by a clear image similar to the main reading step. Therefore, the reading state of the sensor can be confirmed accurately.

  Further, in this sensor, the provisional reading process and the main reading process are performed by the same backlight unit 111, sensor unit 113, signal processing unit 115, and CPU 117.

Therefore, as compared with the configuration including two sensor units for the temporary reading process and the main reading process, there is no deviation in the image reading state between the temporary reading process and the main reading process.
For this reason, if the result of the temporary reading process is good, the main reading process can be performed similarly (that is, the reliability of the temporary reading process can be improved).

  Further, it is possible to avoid an increase in cost and an increase in the overall size due to the provision of the two sensor units.

  Further, in this sensor, as shown in steps S21 and S22 in FIG. 14, the temporary reading process is repeatedly performed until the CPU 117 receives an instruction from the user (instruction for shifting to the color mode (main reading process)). It is set.

  Therefore, the user can continuously perform the provisional reading process while changing the reading state of the sensor (the position of the sensor unit 113 with respect to the document).

  That is, by repeating the high-speed temporary reading process, it is possible to adjust the reading state (alignment of the sensor unit 113) while displaying monochrome original image data continuously (in almost real time). Therefore, the time required for the temporary reading process can be shortened.

  Further, in the present sensor, when color original image data is generated in the main reading process, the backlight unit 111 irradiates the original with red, green, and blue light one by one. Then, the CPU 117 generates document image data of each color and then combines them to generate color document image data.

  That is, in this reading process, the CPU 117 generates a plurality of single-color document image data in a time division manner and synthesizes them. Accordingly, the time required for the provisional reading process for generating only single-color document image data can be significantly accelerated as compared with the main reading process (can be reduced to about one third).

  The sensor is a contact type two-dimensional image sensor (area sensor) that reads an image of a document two-dimensionally and does not require mechanical scanning. Therefore, the time required for the temporary reading process and the main reading process can be shortened as compared with the line sensor.

  In the scanner using the line sensor, even if the resolution is lowered, it takes several seconds to operate the line sensor in order to acquire the document image data by the provisional reading process. Therefore, it is difficult to continuously display the document image data in the temporary reading process.

  Further, in this sensor, the sensor unit 113 is disposed on the backlight unit 111. Then, the light transmitted through the backlight unit 111 is reflected by the manuscript and irradiated on the sensor unit 113. For this reason, it is not necessary to use an optical system for light irradiation on the document and the sensor unit 113. For this reason, this sensor is a small, thin, and light area sensor.

  Further, in this sensor, the backlight unit 111 is set so that light of three primary colors of red, green, and blue can be irradiated onto the document. As a result, it is possible to obtain original document image data of natural colors (original document image data that faithfully reproduces the document image).

  In the temporary reading process, the backlight unit 111 irradiates the original with green light. Green is a color located in the center of the visible region of light, and is easy for the user to visually recognize. Therefore, the user can easily confirm the reading state of the document in the provisional reading process.

  In the present sensor, it is preferable to use a photosensor having good sensitivity in the visible light region. In other words, as a semiconductor (photoelectric conversion material) constituting the photosensor, it is preferable to use a material in which the peak of sensitivity is matched with the middle color (green) in the visible light region. For example, it is preferable to use an amorphous silicon semiconductor used for a phototransistor that has a peak sensitivity in green.

  Thus, by executing the provisional reading process using green monochromatic light corresponding to the peak sensitivity, it is possible to efficiently acquire monochromatic document image data. In addition, it is possible to reduce power consumption, improve S / N, or improve the light receiving speed (reading speed) in the temporary reading process.

  In this sensor, the CPU 117 processes the pixel data transmitted from the signal processing unit 115 to generate document image data. Here, the CPU 117 is preferably provided with a memory for temporarily storing pixel data and document image data. Further, the CPU 117 may be provided with a DSP (Digital Signal Processor). Then, the CPU 117 may generate document image data from pixel data using a DSP.

  In the present embodiment, the CPU 117 generates color document image data by synthesizing three color document image data.

  However, the present invention is not limited to this, and the CPU 117 may transmit the generated three-color document image data to the PC, and the PC may combine these to generate and display color document image data.

  In this sensor, the CPU 117 may set the resolution characteristics of the image data acquired in the temporary reading process to be equal to the resolution characteristics of the image data acquired in the main reading process. As a result, test accuracy (such as document alignment accuracy) in the provisional reading process can be improved. Here, the resolution characteristic is the number of pixels per unit area (or unit length), and is generally expressed in units such as dpi (dots per inch).

  In the present embodiment, if it is determined in S24 of FIG. 14 that a desired portion of the document is read, the user instructs the PC to generate color document image data.

  Here, this instruction is performed by pressing a button for shifting to the color mode on the PC, or by clicking the color mode button of the control software (software for driving this sensor) shown on the PC screen. It is done by doing.

  In the present embodiment, if it is determined in S24 of FIG. 14 that the desired portion of the document has not been read, the CPU 117 returns the process to S21. However, the present invention is not limited to this, and the process may be returned to S22 or S23.

In the present embodiment, it is determined in S22 and S24 in FIG. 14 whether or not the sensor unit 113 has read a desired portion of the document. This is actually a determination as to whether or not the pixel formation region (region where the photosensor (light receiving pixel) is formed) in the sensor unit 113 faces a desired portion of the document.
In S22 and S24, in addition to the above determination, it is also preferable to determine whether the orientation of the sensor unit 113 (the pixel formation region of the sensor unit 113) and the desired portion of the document is appropriate.

  If the size of the pixel formation area in the sensor unit 113 is larger than the original, the reading range by this sensor may be confirmed in S22 and S24. That is, in this case, the CPU 117 sets the reading range so that only a desired portion of the document is read by the sensor unit 113 in accordance with a user instruction via the PC. In S21 and S23, the CPU 117 displays the reading range to the user via the PC. In S22 and S24, the CPU 117 generates monochrome document image data within the reading range designated by the user until the user determines that the reading range is appropriate.

  Similarly, the resolution or resolution of the image may be set in S21 or S23. In this case, the CPU 117 generates monochrome document image data at the resolution or resolution designated by the user until the user's desired resolution or resolution can be set.

  In this sensor, the backlight unit 111 includes an LED 123 (three-color LED), and image reading is performed using the light. However, the light emitting elements that can be used in the backlight unit 111 are not limited to LEDs. Any light emitting element such as an EL light emitting element can be used as long as the backlight unit 111 can emit single color light and can emit light of three colors (R, G, B). But it can be applied.

  In this embodiment, the sensor is a contact-type two-dimensional image sensor (area sensor) that reads a document image two-dimensionally and does not require mechanical scanning. However, this sensor can also be configured as a scanner of a type that scans a document image with a line sensor.

  That is, when this sensor is configured as a scanner, in provisional reading (pre-scan), an image is read by irradiating light from only one color light emitting element in the line sensor to generate monochrome document image data. Thereafter, in the main reading (main scanning), light is emitted from the light emitting elements of the three colors in the line sensor to read the image, and color original image data is generated.

  Even with this configuration, the time required for provisional reading can be reduced to about one-third that of the main reading. In addition, since the temporary reading and the main reading are performed using one sensor, it is possible to prevent the difference in the read image due to the difference in sensor between the two types of reading.

  In the present embodiment, it is assumed that in the temporary reading, the original is irradiated with green light from the backlight unit 111, and the CPU 117 generates green original image data. However, the color of light used for provisional reading is not limited to this, and may be blue or red.

  Here, an LED that emits light used for provisional reading (for example, a green LED (light emitting element)) has a longer total use time than an LED of another color. For this reason, it is preferable to use light emitted from an LED having a long lifetime as light used for provisional reading.

  Further, the color of light used for temporary reading may be switched every time it is used. For example, a sequence may be incorporated so that the CPU 117 switches the color of light used in the provisional reading process every time the power of the sensor is turned on again by the user (when the sensor is turned on from the OFF state). Good. Thereby, the usage time of LED of each color is averaged and the malfunction which only specific LED (light emitting element) deteriorates in a short period can be avoided.

Further, the CPU 117 may change the color used for provisional reading in accordance with a user instruction. Here, when single-color light having a color close to that often used in document images is used, document image data obtained by provisional reading can be made clearer.
In addition, in the temporary reading process, if light having a high light emission intensity or light of a color received by the sensor unit 113 with relatively high sensitivity is used, the document image data generation process can be accelerated (or temporarily read). Can reduce the amount of irradiation light).

  Further, in order to obtain monochrome document image data in the provisional reading step, mixed color light (mixed with light having different wavelengths) may be used instead of monochromatic light.

  Such mixed color light can be generated by simultaneously irradiating light from two or more LEDs among the three color LEDs of the backlight unit 111. For example, when light is irradiated from all the LEDs simultaneously, white mixed light can be irradiated onto the document.

  Monochrome image data can also be acquired by reading the reflected light obtained by irradiating the original with such mixed color light by the sensor unit 113.

  As described above, in this sensor, monochrome document image data can be acquired by monochromatic light or mixed color light in the provisional reading process. Note that when monochromatic light is used, power consumption in the provisional reading process can be reduced. On the other hand, when mixed color light is used, the amount of light can be increased because light is emitted from three LEDs. Therefore, it is possible to improve the light receiving characteristics (S / N and light receiving speed) by the sensor unit 113 (photo sensor).

  Further, in the present embodiment, in the main reading, red, green, and blue light from the backlight unit 111 is sequentially irradiated onto the document, and the CPU 117 generates color document image data.

  However, the present invention is not limited to this, and the present sensor may be configured to emit light of three colors other than these, or may be configured to emit light of two colors or four colors or more.

  In other words, this sensor may be set so as to generate monochrome document image data by provisional reading, while generating original document data having more colors (monochrome) than monochrome by actual reading. In this case, natural color original image data (original image data faithfully reproducing the original image) may not be obtained in the actual reading. However, even in this case, original image data with more information (number of colors) can be obtained in the main reading than in the temporary reading.

In the present embodiment, the sensor is connected to the PC, and the user sends an instruction to the sensor using the PC input unit (via the PC).
However, the present invention is not limited to this, and the sensor may be provided with an input unit that receives an instruction from the user, and the user's instruction may be transmitted to the CPU 117 via the input unit.

  In the present embodiment, the document image data generated by this sensor is displayed on the display unit of the PC. However, the present invention is not limited to this, and the sensor may be provided with a display screen, and the original image data may be displayed on this screen.

  As described above, when the sensor includes the input unit and the display screen, it is not necessary to connect the sensor to the PC.

  For example, the sensor may have a plate shape, and one surface may be an image reading surface (a surface on which a protective film is formed), and a display screen for displaying image data may be provided on the other surface (back surface). Good.

  When the sensor has a plate shape as described above, the sensor is placed on the document with the document reading surface facing the document. In the temporary reading process, the user adjusts the position of the sensor while looking at the display screen on the back side of the document reading surface. As a result, the user can confirm the actual state of the original by looking at the display screen immediately above it (the original and the display screen can be observed on the same line of sight). Therefore, user operability can be improved (positioning of the sensor and the document can be easily performed).

  In the above description, the gate voltage is set in advance so that the optimum sensitivity is obtained according to the readout speed and the amount of irradiation light, and the condition at that time out of the set gate voltage when the thin film transistor is in the non-conductive state and when receiving light. A two-dimensional image sensor that selects a gate voltage according to (reading speed and irradiation light amount) and applies the selected gate voltage to the gate electrode of the thin film transistor has been described.

  That is, in this case, for example, two types of Vgl values are prepared (for alignment and for actual reading) (this voltage is set to a standard value at the time of product shipment, and the user sets these two types. The image may be read quickly with a high voltage Vgl for image alignment. After this alignment, the main reading is performed at a low voltage Vgl.

  The present invention is not limited to this. For example, when the thin film transistor is in a non-conducting state and when receiving light, the reading speed and the amount of irradiation light are detected, and a gate voltage that provides optimum sensitivity based on the detected value. And the gate voltage may be applied to the gate electrode of the thin film transistor.

  That is, in this case, provisional reading is performed with a high reading speed set by Vgl of a higher voltage (same as prescan of an existing scanner), and based on this value, the dynamic range of black and white difference is increased. , Vgl voltage and irradiation time are determined. The determination of Vgl and the irradiation time at this time is performed based on the Vgl control signal by a Vgl control unit in an external circuit provided outside the two-dimensional image sensor, as shown in FIG.

  As described above, the photoelectric conversion device according to the present embodiment charges the auxiliary capacitor 17 connected to the drain D of the TFT 7 having the photosensitive semiconductor layer by a predetermined amount as shown in FIG. After the capacitor 17 has been charged with a predetermined amount of charge, the TFT 7 is turned off, the photosensitive semiconductor layer is irradiated with light for a predetermined time, and the photosensitive semiconductor layer is irradiated with light for a predetermined time. A device for detecting the photoelectric conversion amount of the sensor substrate 20 including the TFT 7 based on the charge of the capacitor 17 when the TFT 7 is in a non-conductive state and the photosensitive semiconductor layer is irradiated with light for a predetermined time. A driving IC 19 for applying a gate voltage to the gate G of the TFT 7 and a control / communication board as a gate voltage control means for variably controlling the gate voltage applied by the driving IC 19 It is equipped with a 4.

  According to the above configuration, a gate voltage that is variably controlled is applied to the gate G by the control / communication substrate 24 when the TFT 7 is turned off and the photosensitive semiconductor layer is irradiated with light for a predetermined time. As a result, the detected photoelectric conversion amount can be controlled.

  As a result, a detected photoelectric conversion amount, that is, a gate voltage that maximizes the photocurrent flowing through the non-conducting TFT 7 can be applied to the gate G of the TFT 7, so that a sufficient photoelectric conversion amount can be obtained. That is, a photoelectric conversion device that can obtain optimum sensitivity can be realized.

  In this case, the control / communication board 24 sets the gate voltage to a value at which the maximum photocurrent can be obtained within the time in which the TFT 7 is turned off and the photosensitive semiconductor layer is irradiated with light. What should I do?

  The value of the gate voltage set by the gate voltage control means is a value derived from the relationship between the irradiation time of light to the thin film transistor and the photoelectric conversion amount at that time when the thin film transistor is turned off. May be.

  Specifically, from the sensitivity characteristic graphs and photocurrent characteristic graphs as shown in FIGS. 17 to 19, the gate voltage at which the maximum sensitivity is obtained by each reading speed and each mode is obtained, and the obtained gate voltage is obtained. The voltage control unit 101 in the control / communication board 24 may be controlled so as to be a voltage. That is, the voltage control unit 101 performs control so as to obtain an optimum gate voltage based on the signal from the reading speed switching signal generation unit 102 and the signal from the mode switching signal generation unit 103.

  Further, by adopting a configuration as shown in FIG. 16, it is possible to set an optimum gate voltage that maximizes sensitivity in real time. That is, the control / communication board 24 causes the drive IC 19 to apply a reference gate voltage (applicable maximum gate voltage) to the gate G of the TFT 7, and based on the photoelectric conversion amount detected at that time, the gate G Sets the value of the gate voltage to be applied to.

  In addition, the photoelectric conversion method according to the present invention provides a gate voltage that maximizes the amount of photoelectric conversion detected when the TFT 7 is turned off and light is applied to the photosensitive semiconductor layer constituting the TFT 7 for a predetermined time. Is applied to the gate G of the TFT 7.

  According to the above configuration, when the TFT 7 is turned off and the photosensitive semiconductor layer is irradiated with light for a predetermined time, a gate voltage that maximizes the detected photoelectric conversion amount is applied to the gate G of the TFT 7. When applied, the detected photoelectric conversion amount, that is, the photocurrent flowing through the non-conducting TFT 7 is maximized.

  Accordingly, it is possible to provide a photoelectric conversion method capable of obtaining the maximum sensitivity (photoelectric conversion amount) with an appropriate gate voltage corresponding to the light irradiation amount (irradiation time × light intensity) to the non-conducting TFT 7. it can.

  In the image reading apparatus using the above configuration, a plurality of the photoelectric conversion devices described above are arranged corresponding to the document image, and the photoelectric conversion amount of the sensor substrate 24 detected by each photoelectric conversion device is used as the input image of the document image. It is the structure which outputs as information.

  According to the above configuration, since the photoelectric conversion device described above is provided, a sufficient amount of photoelectric conversion can be obtained, and as a result, optimum sensitivity corresponding to the reading speed of the document and the amount of light applied to the document can be obtained. it can.

  Thereby, input image information faithful to the original image can be output.

  Further, the document image includes a backlight unit 18 that irradiates red light, green light, and blue light, respectively, and the amount of photoelectric conversion of the sensor substrate 20 detected according to the irradiation light of each color by the backlight unit 18. The input image information may be output as a color image.

  In this case, the gate voltage for obtaining the optimum sensitivity (photoelectric conversion amount) differs between the operation at the time of monochromatic light, that is, when the reading speed is high, and the operation at the time of multicolor light, that is, when the reading speed is low. If the gate voltage to be applied is changed between the operation for monochromatic light and the operation for multicolor light by the control / communication board 24 of the conversion device, the photoelectric conversion amount in each case can be maximized. It becomes.

  In this embodiment, the two-dimensional image sensor in which the photoelectric conversion device is two-dimensionally arranged in the image reading device having the above-described configuration has been described. However, the photoelectric conversion device may be one-dimensionally arranged.

  As described above, when the photoelectric conversion device is arranged one-dimensionally, it can be suitably used for a portable image input device such as a handy scanner used in a home facsimile device.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  Since the present invention can read an original faithfully, it can be applied particularly to an image reading apparatus such as an image scanner that requires reading accuracy, and since it does not have a mechanical scanning mechanism, the apparatus can be downsized. It can also be applied to handy-type scanners.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates an embodiment of the present invention, and is a block diagram illustrating a main configuration of a photoelectric conversion device. FIG. 2 is a schematic cross-sectional view of the photoelectric conversion device shown in FIG. 1. It is a graph which shows the gate voltage-drain current characteristic in the photoelectric conversion apparatus shown in FIG. It is a schematic block diagram of the two-dimensional image sensor using the photoelectric conversion apparatus shown in FIG. FIG. 6 is a schematic perspective view of the two-dimensional image sensor shown in FIG. 5. It is a timing chart which shows the detection operation in the photoelectric conversion apparatus shown in FIG. It is a flowchart which shows the flow of operation | movement in the two-dimensional image sensor concerning one Embodiment of this invention. It is a timing chart which shows operation | movement of the two-dimensional image sensor concerning one Embodiment of this invention. It is a schematic circuit diagram of the gate driver applied to the two-dimensional image sensor concerning one Embodiment of this invention. FIG. 10A is a timing chart showing an example of the operation of the gate driver when the outputs of the gate driver shown in FIG. 9 are collectively turned on, and FIG. 10B is the gate driver shown in FIG. 12 is a timing chart showing another example of the operation of the gate driver when the outputs of are collectively turned on. 6 is another timing chart showing the operation of the photoelectric conversion device shown in FIG. 1. It is a block diagram which shows the structure of the other two-dimensional image sensor of this invention. It is sectional drawing which shows the structure of the backlight part and sensor part in the two-dimensional image sensor shown in FIG. 13 is a flowchart showing a flow of composite image reading processing in the two-dimensional image sensor shown in FIG. 13 is a timing chart showing the operation of the two-dimensional image sensor shown in FIG. In the photoelectric conversion apparatus of this invention, it is a block diagram which shows schematic structure for the setting of a gate voltage. It is a graph which shows the sensitivity characteristic by the gate voltage change applied to the thin-film transistor of a non-conduction state. It is a graph which shows the sensitivity characteristic by the gate voltage change applied to the thin-film transistor of a non-conduction state. It is a graph which shows the photocurrent characteristic by the gate voltage applied to the thin-film transistor of a non-conduction state, and light quantity change.

Explanation of symbols

1 Document 2 Irradiation Light 3 Protective Film 4 Silicon Layer 6 Opening 7 TFT (Thin Film Transistor)
9 Insulating substrate 10 Source electrode 11 Bottom gate electrode 12 Semiconductor layer 13 Bottom gate insulating film 14 Insulating film 15 Drain electrode 17 Auxiliary capacitor 18 Backlight unit 19 Driving IC (gate voltage applying means)
20 Sensor substrate (photoelectric conversion element)
21 Driving Printed Circuit Board 22 Gate Line 23 Data Line 24 Control / Communication Board (Gate Voltage Control Unit)
25 Detection IC
26 detection printed circuit board 28 drive circuit 29 detection circuit 30 reset switch 31 control unit 32 reference voltage 33 integration amplifier 34 low-pass filter 35 amplification amplifier 36 sample hold circuit 37 analog multiplexer 38 A / D conversion circuit 39 feedback capacitor 40 CS electrode drive voltage 41 Parasitic capacitance 51 Shift register 52 AND gate 101 Voltage control unit 102 Reading speed switching signal generation unit 103 Mode switching signal generation unit 111 Backlight unit 112 LED control unit 113 Sensor unit 114 Sensor control unit 115 Signal processing unit 116 External interface 117 CPU
121 Condensing lens sheet 122 Light scattering plate 123 LED
124 Light guide 131 Transparent substrate 132 Photosensor group 133 Photosensor D Drain G Gate S Source P Document Vcs CS electrode drive voltage Vgl Gate voltage Vref Reference voltage

Claims (16)

The auxiliary capacitor connected to the drain electrode of the thin film transistor having the photosensitive semiconductor layer is charged with a predetermined amount of charge, and after the charging of the predetermined amount of charge to the auxiliary capacitor is completed, the thin film transistor is made non-conductive and the photosensitive semiconductor In a photoelectric conversion device for detecting a photoelectric conversion amount of a photoelectric conversion element including the thin film transistor based on a charge of the auxiliary capacitor after irradiating the layer with light for a predetermined time and irradiating the photosensitive semiconductor layer with light for a predetermined time ,
Gate voltage applying means for applying a gate voltage to the gate electrode of the thin film transistor when the thin film transistor is turned off and the photosensitive semiconductor layer is irradiated with light for a predetermined time;
And a gate voltage control means for variably controlling the gate voltage applied by the gate voltage application means. Within a time period in which a plurality of thin film transistors are in a non-conductive state and each photosensitive semiconductor layer is irradiated with light having different intensities, the photocurrent value of the thin film transistor irradiated with the strongest light or the accumulated value thereof, When the maximum sensitivity is the difference between the photocurrent value of the thin film transistor irradiated with the weakest light or the accumulated value,
The gate voltage control means includes
2. The photoelectric device according to claim 1, wherein the gate voltage is set to a value at which maximum sensitivity can be obtained within a time during which the thin film transistor is turned off and light is applied to the photosensitive semiconductor layer. Conversion device.   The value of the gate voltage set by the gate voltage control means is a value derived from the relationship between the irradiation time of light to the thin film transistor and the photoelectric conversion amount at that time when the thin film transistor is turned off. The photoelectric conversion device according to claim 2. The gate voltage control means includes
A reference gate voltage is applied to the gate electrode of the thin film transistor by the gate voltage applying means, and a value of the gate voltage applied to the gate electrode is set from the photoelectric conversion amount detected at that time. Item 3. The photoelectric conversion device according to Item 2. The auxiliary capacitor connected to the drain electrode of the thin film transistor having the photosensitive semiconductor layer is charged with a predetermined amount of charge, and after the charging of the predetermined amount of charge to the auxiliary capacitor is completed, the thin film transistor is made non-conductive and the photosensitive semiconductor In a photoelectric conversion method of detecting a photoelectric conversion amount of a photoelectric conversion element including the thin film transistor based on the charge of the auxiliary capacitor after irradiating the layer with light for a predetermined time and irradiating the photosensitive semiconductor layer with light for a predetermined time ,
Within a time period in which a plurality of thin film transistors are in a non-conductive state and each photosensitive semiconductor layer is irradiated with light having different intensities, the photocurrent value of the thin film transistor irradiated with the strongest light or the accumulated value thereof, When the maximum sensitivity is the difference between the photocurrent value of the thin film transistor irradiated with the weakest light or the accumulated value,
A photoelectric conversion method, comprising: applying a gate voltage having a maximum sensitivity to a gate electrode of the thin film transistor when the thin film transistor is in a non-conducting state and the photosensitive semiconductor layer is irradiated with light for a predetermined time. The photoelectric conversion device according to claim 1, wherein a plurality of the photoelectric conversion devices are arranged corresponding to a document image;
An image reading apparatus comprising: an image information output unit that outputs a photoelectric conversion amount of a photoelectric conversion element detected by each photoelectric conversion apparatus as input image information of a document image. A light irradiating means for irradiating the original image with red light, green light, and blue light, respectively,
The image according to claim 6, wherein the image information output unit outputs the input image information as a color image from the photoelectric conversion amount of the photoelectric conversion element detected according to the irradiation light of each color by the light irradiation unit. Reader.   The image reading apparatus according to claim 6, wherein the photoelectric conversion devices are arranged one-dimensionally.   The image reading apparatus according to claim 6, wherein the photoelectric conversion device is two-dimensionally arranged.   The image reading apparatus according to claim 6, wherein the charge to the auxiliary capacitors is performed all at once. Multiple data lines,
A plurality of scan lines intersecting the data lines;
A photoelectric conversion element including a thin film transistor having a photosensitive semiconductor layer provided at each intersection of the data line and the scanning line, and an auxiliary capacitor connected to a drain electrode of the thin film transistor and charged with charge;
A photoelectric conversion amount detecting means connected to the source electrode of the thin film transistor for detecting the photoelectric conversion amount by the thin film transistor;
Image information output means for outputting the result detected by the photoelectric conversion amount detection means as image information,
The auxiliary capacitor is charged with a predetermined amount of charge, and when the thin film transistor is in a non-conductive state, the charge is discharged by light irradiation to the photosensitive semiconductor layer,
The photoelectric conversion amount detection means is a two-dimensional image sensor that detects the photoelectric conversion amount of the photoelectric conversion element based on the charge of the auxiliary capacitor after the light irradiation to the photosensitive semiconductor layer is completed,
Gate voltage applying means for applying a gate voltage to the gate electrode of the thin film transistor when the thin film transistor is turned off and the photosensitive semiconductor layer is irradiated with light for a predetermined time;
A two-dimensional image sensor comprising gate voltage control means for variably controlling the gate voltage applied by the gate voltage application means.   The two-dimensional image sensor according to claim 11, wherein the data line, the scanning line, the thin film transistor, and the auxiliary capacitor are formed on a transparent substrate.   The two-dimensional image sensor according to claim 11, wherein a transparent protective layer is formed on a surface of the transparent substrate on a side where the thin film transistor is formed.   A light irradiating means is provided on the surface of the transparent substrate opposite to the thin film transistor forming surface, and the irradiated object disposed on the thin film transistor forming surface is irradiated with light, and the reflected light from the irradiated object is irradiated. The two-dimensional image sensor according to claim 11, wherein the thin film transistor is irradiated. A light irradiation control means for controlling the light irradiation of the light irradiation means,
The light irradiation control means controls the light irradiation means to irradiate light for a predetermined time after a predetermined amount of charge is charged in the auxiliary capacitor,
The photoelectric conversion amount detection means detects the photoelectric conversion amount by the photoelectric conversion element based on the charge of the auxiliary capacitor in a state where light irradiation is stopped after light irradiation by the light irradiation means for a certain time. The two-dimensional image sensor according to claim 11. The method for driving a two-dimensional image sensor according to claim 10,
Within a time period in which a plurality of thin film transistors are in a non-conductive state and each photosensitive semiconductor layer is irradiated with light having different intensities, the photocurrent value of the thin film transistor irradiated with the strongest light or the accumulated value thereof, When the maximum sensitivity is the difference between the photocurrent value of the thin film transistor irradiated with the weakest light or the accumulated value,
After all the auxiliary capacitors connected to the thin film transistors are charged with a predetermined amount of charge, the scanning lines are driven to sequentially turn on the thin film transistors, and the photoelectric conversion elements are based on the charges of the auxiliary capacitors. Detecting the photoelectric conversion amount by
In the step, when the thin film transistor is turned off and the photosensitive semiconductor layer is irradiated with light for a predetermined time, a gate voltage that provides maximum sensitivity is applied to the gate electrode of the thin film transistor. A driving method for a two-dimensional image sensor.

Images